ddd installation on MacBook Pro Mac OS X 10.6.8

Hi, 

I am trying to install ddd on my laptop MacBook Pro (Mac OS X 10.6.8).

From " http://ftp.gnu.org/gnu/ddd/ " , I downloaded "ddd-3.3.12.tar.gz", and saved it in Application 
folder.
Then I followed the instructions.

1. Unpack the DDD source distribution
2. Change into the ddd-3.3.12
3. Type ./configure && make

Then, I get an error message.

configure: error: The Motif include file 'Xm/Xm.h' could not be found.
                  Please use the configure options '--with-motif-includes=DIR'
                  and '--with-motif-libraries=DIR' to specify the Xm location.
                  See the files 'config.log' and 'ddd/config.log'
                  for further diagnostics.
make: *** No targets specified and no makefile found.  Stop.

I would appreciate if someone could help me.

Best Regards,

Sonoko